lkml.org 
[lkml]   [2009]   [Aug]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [patch] ext2/3: document conditions when reliable operation is possible

    > While I think it is, in principle, worth documenting this sort of
    > thing, there are an awful lot of fine details and distinctions that
    > would need to be considered.

    Ok, can you help? Having a piece of MD documentation explaining the
    "powerfail nukes entire stripe" and how current filesystems do not
    deal with that would be nice, along with description when exactly that
    happens.

    It seems to need two events -- one failed disk and one powerfail. I
    knew that raid5 only protects against one failure, but I never
    realized that simple powerfail (or kernel crash) counts as a failure
    here, too.

    I guess it should go at the end of md.txt.... aha, it actually already
    talks about the issue a bit, in:

    #Boot time assembly of degraded/dirty arrays
    #-------------------------------------------
    #
    #If a raid5 or raid6 array is both dirty and degraded, it could have
    #undetectable data corruption. This is because the fact that it is
    #'dirty' means that the parity cannot be trusted, and the fact that it
    #is degraded means that some datablocks are missing and cannot reliably
    #be reconstructed (due to no parity).

    (Actually... that's possibly what happened to friend of mine. One of
    disks in raid5 stopped responding and whole system just hanged
    up. Oops, two failures in one...)
    Pavel

    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


    \
     
     \ /
      Last update: 2009-08-26 01:49    [W:7.271 / U:0.020 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site